Liquid developer for electrophotograph

ABSTRACT

WHEREIN R1 and R2 each represents -H or -CH3, X represents COOCnH2n 1 (6 &lt; OR = n &lt; OR = 20), and Y represents -CONHCH2OH, CONHCH2OCH3, -CONHCH2OC2H5, -CONHCH2OC3H7, -CONHCH2OC4H9, CONHCH2OC5H11 A stable liquid developer for electrophotography contains in a carrier having high electric resistance and low dielectric constant a toner prepared by graft polymerizing the additionpolymerizable compound shown by the following formula (I), the addition-polymerizable compound shown by the following formula (II), and pigment particles;

United States Patent 1191 Tamai et al.

[ LIQUID DEVELOPER FOR ELECTROPHOTOGRAPH [75] Inventors: Yasuo Tamai, Odawara; Sadao Osawa, Asaka; Satoru Honjo, Asaka; Akira Umehara, Asaka; Masaya Yamamoto, Tokyo; Nobuo Tsuji, Ashigara; Naomitsu Takashina, Fujisawa; Wakio Nagashima, Kanagawa, all of Japan [731 Assignees: Fuji Photo Film Co., Ltd., Ashigara; Mitsubishi Gas Chemical Company, Incorporated, Tokyo, both of Japan [22] Filed: June 15, 1973 [2]] Appl. No.: 370,212

[30] Foreign Application Priority Data June 16,1972 Japan 47-60110 [52] U.S.Cl ..252/62.1;260/66;260/33.6 UA [51] Int. Cl ..G03g 9/04 [58] Field of Search 252/62.1;260/66, 33.6 UA

[56] References Cited UNITED STATES PATENTS 3,544,946 1/1971 Okunoetal. ..252/62.l 3,639,244 1/1972 Machidaetal. ..252/62.1 3,668,127 6/1972 Machidaetal. ..252/62.l

1 C0NH-C|J-CH -(i-CH CH 0 Primary Examiner-Norman G. Torchin Assistant Examiner-Jack P. Brammer Attorney, Agent, or Firm-Gerald J. Ferguson, Jr.; Joseph J. Baker 1 51 May 13, 1975 [5 7] ABSTRACT A stable liquid developer for electrophotography contains in a carrier having high electric resistance and low dielectric constant a toner prepared by graft polymerizing the addition-polymerizable compound shown by the following formula (I), the addition-polymerizable compound shown by the following formula (II), and pigment particles;

CH (I;

wherein R and R each represents H or Cl-l X represents COOC, l-l (6 S n s 20), and Y represents CONHCH OH, CONHCH OCH -CONHCH OC H CONHCH OC H CONHC- H OC H CONHCH OC l-l 401111013 N 0 or -co N o 11 Claims, No Drawings LIQUID DEVELOPER FOR ELECTROPHOTOGRAPH BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a novel composition for an electrophotographic liquid developer, more particularly, to an improved electrophotographic liquid developer containing positively charged fine toner particles.

2. Description of the Prior Art Among developers for converting electrostatic latent images formed by an electrophotographic method or an electrostatic recording method into visible images or images of materials, a developer comprising fine particles suspended in an electrically insulating liquid is called a liquid developer, and when such a liquid developer is employed, a visible image having high sharpness and high resolving power as compared with the case of using other developers can be obtained, and further an electrostatic latent image having low contrast can be effectively converted into a visible image. Also, in the case of a liquid developer, developer particles having a small particle size can be easily obtained, and thus the liquid developer is preferably used for obtaining a photograph of continuous tone.

A conventional liquid developer is composed of a suspension of particles of a pigment or dye such as Phthalocyanine Blue, carbon black, and Nigrosine dyes in an electrically insulating carrier liquid. However, when the particles of a pigment or a dye are suspended in an insulating carrier liquid, it is usually difficult to keep a charge of the desired polarity on the particles in the liquid developer. Thus, for controlling the electrostatic charge on the particles of pigment or dye in the liquid developer, a method has ordinarily been adopted where a resin or a polarization control agent, each capable of being dissolved in the insulating liquid, is added to the insulating liquid or an insulating resin which is soluble or insoluble in the insulating liquid and coats the surface of the pigment or dye particles is added to the insulating liquid.

In the above-described liquid developer, the polarization control agent or the resin is comparatively strongly adsorbed on the particles of pigment or dye directly after the preparation of the liquid developer or a short period of time after the preparation of the developer, and thus the pigment or dye particles are in a well dispersed state and maintain a stable charge as a toner directly after dispersing the pigment particles. However, in the case of using such a conventional liquid developer, it usually happens that with the passage of time the adsorbed material on the pigment or dye particles is gradually released therefrom to degrade the dispersibility of the particles and the polarization control power of the material, and thus the liquid developer cannot maintain for long periods of time its developing capability gained at the preparation of the developer.

One attempt to overcome the aforesaid faults provides a graft carbon type liquid developer. The term graft carbon (the registered trade name of a product made by Mitsubishi Gas Chemical Co., Ltd.) means a product prepared by the graft polymerization of a vinylic polymer onto the surface of pigment particles, in particular carbon black particles. Graft carbon is described in detail and its preparation in, for instance, Nippon Gomu Kyokai-Shi (Journal of the Rubber So- 2 ciety of Japan), Vol. 38, January, pages 13-22; Kobunshi (Polymer)", Vol. 17, pages 822-827, U.S. Pat. No. 3,557,040; and Japanese Patent Publication 17284/ 1970.

It is also known that the graft carbon be used as a toner in electrophotography. For instance, the use of graft carbon as a toner is described in detail in Kobunshi (Polymer)", Vol. 14, September, 746 and 749 (1965) and the Pamphlet About Graft Carbon, page 3 published by Nippon Gas Chemical Industries Co., Ltd. Various electrophotographic liquid developers containing graft carbon are disclosed in, e.g., Japanese Patent Publications 27597/1968, 19196/1969, 6151/1971, 6152/1971, 6155/1971, 6156/1971, 8278/1971, 6157/1971, 4438/1972 and 4439/1972.

It has, however, been confirmed that liquid developers as disclosed in the aforesaid publications are not always sufficient. For instance, in the case of the invention described in Japanese Patent Publication 27597/1968 it is difficult to disperse the graft carbon in the isoparaffinic liquid carrier, and also in the case of the invention described in Japanese Patent Publication 19196/1969 toner particles dispersed in the carrier liquid do not have a charge of definite polarity.

The liquid developers disclosed in the other patents indicated above do not give sufficiently high image densities. When electrostatic latent images formed on zinc oxide-type photosensitive layers are developed by the liquid developers described in the abovementioned patents, the maximum reflection optical densities of the images of the samples are in the range of 1.35-1.65. Since the maximum reflection optical density of an ordinary original to be duplicated is higher than 2, good duplications cannot be obtained using such conventional liquid developers.

Further, in the patents described above, monomers for improving the dispersion of a toner in a carrier liquid (hereinafter called dispersing monomers) and monomers for providing a charge on the toner (hereinafter called polarization monomers) are used together. However, in the case of providing a sufficient charge on a toner, a large proportion of the polarization monomer must be copolymerized, which results in reducing the dispersibility of the toner.

Also, when a liquid developer is prepared by dispersing the graft carbon in a carrier liquid immediately after the production thereof (in such a case the graft carbon is usually in the form of a viscous paste), a liquid developer having a better developing property can be obtained, but when a liquid developer is prepared by using graft carbon stored for a long period of time after the preparation thereof, the dispersibility of the graft carbon frequently is inferior. This phenomenon is particularly remarkable when the graft carbon is stored for a long period of time at a high temperature. The reason therefore has not yet been ascertained, but is is believed there are problems on the selection of the polarization monomer to be copolymerized with the dispersing monomer. That is to say, it is considered that the stability of the polarization monomer in the copolymer or the co-action of the polarization monomer is related to the aforesaid phenomenon.

Moreover, it has also been discovered that the images obtained by using toners having polarization monomer components as proposed in the aforesaid various reports are deficient in weathering resistance, although the reason is also considered to be based on the insta- LII bility of the polarization monomer portion. In particular, this problem becomes serious when marking is electrophotographically applied to a steel plate and then the steel plate having the image thus marked is exposed to the direct rays of the sun for a long period of time.

SUMMARY OF THE INVENTION Thus, an object of this invention is to provide a toner for a liquid developer having excellent stability, in particular, having an excellent storageproperty in the graft-copolymerized state or in the state before use in a liquid developer.

Another object of this invention is to provide a liquid developer containing a toner having a positive charge and capable of giving images superior in weathering resistance.

Still another object of this invention is to provide a liquid developer having excellent dispersibility and capable of giving high image density.

A further object of this invention is to provide a composition of a graft copolymer-type toner capable of yielding a liquid developer of high toner concentration.

According to this invention, there is provided a liquid developer for electrophotography containing, in a carrier liquid having high electric resistance and low dielectric constant, a toner prepared by graft copolymerizing the addition-polymerizable compound represented by the following formula (I), the addition-polymerizable compound represented by the following formula (II), and pigment particles;

CH (I) CONH-C|1-CH -C-CH -CONHCH N or -CO N The graft carbon of the present invention can be prepared according to a conventional procedure such as described in U.S. Pat. No. 3,557,040, and Kogyo Kagaku Zasshi, Vol. 67, No. 2, (1964) using the starting materials of this invention.

DETAILED DESCRIPTION OF THE INVENTION In the present invention, various pigments can be used but pigments such as carbon black, aniline black,

alkali blue, Phthalocyanine Blue, Phthalocyanine Green, etc., give better results. In particular, carbon black is most preferred as the pigment from the point of good graft copolymerizability. The particle size of the pigments is preferably less than I p., most preferably less than 0.4 p"

The addition-polymerizable compound shown in the above-indicated indicated formula (II) is to give a positive charge to toner when it is graft copolymerized. In general, if the proportion of a polarization monomer is too small as compared with the proportion of a dispersing monomer, it is difficult to effectively provide a charge to the toner prepared therefrom, but the compound of formula (II) in this invention, which is a polarization monomer, is excellent in its ability to give polarity to the toner, and hence the compound of the formula (I) can be used in an amount of up to about 45 parts by weight per 1 part by weight of the compound of the formula (II). If the proportion of the compound of the formula (I) is over the aforesaid ratio, the charge of the toner becomes unstable.

When the addition-polymerizable compound of the formula (I) is graft copolymerized, it has the effect of permitting the toner to be well dispersed in a carrier liquid. Accordingly, if the proportion of the compound of formula (I) it too small as compared with the proportion of the compound of formula (II), the dispersibility of the toner is reduced. In the present invention, more than about 5 parts by weight of the compound of the formula (I) is required per 1 part by weight of the compound of the formula (II). If the content of the compound of the formula (I) is less than the value mentioned above, the coagulation of toner occurs in the carrier liquid.

From these results, it has been confirmed that a preferred toner can be obtained by using a combination of 5-45 parts by weight of the addition polymerizable compound of formula (I) and 1 part by weight of the addition polymerizable compound of formula (II).

Further, the addition polymerizable compound of formula (I) in which n is less than 5 gives lowered dispersibility, while the compound of formula (I) in which n is larger than 21 is difficult to obtain, and thus use of such a compound is economically disadvantageous.

On the other hand, it has been found that the ratio of the total amount of the addition polymerizable compound of the formula (I) and the addition polymerizable compound of the formula (II) satisfying the aforesaid condition to the amount of the pigment particles has an influence on the image density, fixing property, etc. That is to say, as the ratio of the total amount of the compound of formula (I) and the compound of formula (II) to the amount of the pigment particles decreases, the image density tends to increase and the fixing property tends to decrease. When the toner is dispersed in such case, the coagulation of the toner does not occur but the toner tends to undergo precipitation. Also, as the total amount of the compound of formula (I) and the compound of formula (II) increases, it has been found that the fixing property increases and the image density obtained is reduced.

As the result of investigations of practical amounts of the pigment to be used, it has been found that the use of the pigment in an amount more than about 6 parts by weight per I part by weight of the total amount of the compound of formula (I) and the compound of formula (II) is undesirable. Also, it has been found that when the pigment is used in an amount less than about 0.2 parts by weight, the image density tends to become lower. The reduction in image density is particularly remarkable when the development period of time is short and the electrostatic contrast is low.

The proper carrier liquid to be used in this invention has an electric resistance higher than about Q.cm. and a dielectric constant less than about 3. There are various materials satisfying the above conditions, e.g., there are straight chain aliphatic hydrocarbons such as octane, nonane, decane, etc.; branched chain aliphatic hydrocarbons such as isooctane, isononane, etc.; aliphatic hydrocarbons such as cyclohexane, decalin, etc.;

, and chlorofluoro-hydrocarbons such as difluorotetrachloroethane, trifluorotrichloroethane etc. However, from an industrial view point, it is desirable to use inexpensive materials such as kerosene, ligroin, mineral spirit, etc. Particularly preferred carrier liquids used in this invention are isoparaffinic mixed solvents. As one such mixed solvent, there is, for instance, the solvent commercially available under the trade name of Isopar from Esso Standard Oil Co.

It is effective to add a small amount of a polarization control agent to the liquid developer of this invention, although the graft-type toner of this invention has, of course, a satisfactorily positive charge without the necessity of the addition of a polarization control agent. However, by adding a polarization control agent, resistance to impurities is increased. This point is particularly important in electrophotographic marking on iron or steel plates in which the prevention of the entrance of impurities is difficult. As the preferred polarization control agents, there are various metal soaps as described in the specification of U.S. Pat. No. 3,259,581, such as manganese linolenate, cobalt naphthenate, manganese resinate, and cobalt oleate and also metal salts of Z-ethylhexonic acid, borates of long chain alcohols, and silicates as described in the specification of Japanese Patent Publication 20868/1966. Furthermore, desirable results are obtained in the case of using the various polarization control agents as are described in the specifications of Japanese Patent Applications 88778/1970, 88779/1970, and 99982/1970. Also, a copolymer of lauryl methacrylate and acrylic acid can be used as the polarization control agent. The amount of the polarization control agent added is generally from about 0.001 to about 5 parts by weight per 1000 parts by weight of the carrier liquid.

In case of using the graft-polymer type toner of this invention, from about 0.1 to about 20 parts by weight of the toner is added to 1000 parts by weight of the carrier liquid, but in particular, the addition of from about 0.5 to about 10 parts by weight of the toner gives higher image density and less fog.

The invention will now be explained in detail by the following examples, in which all parts are by weight unless otherwise indicated.

The mixture of the above components was heated to C for 10 hours in a nitrogen gas atmosphere to give a black, viscous graft carbon copolymer. 8 parts of the copolymer was dispersed in 1000 parts of lsopar H (the trade name of an isoparaffinic solvent made by Esso Standard Oil Co. having an aniline point of 83C, an initial boiling point of 174C, and a dry point of 189C) by ultrasonic waves to provide a liquid developer containing positively charged toner particles.

A zinc oxide type photosensitive paper was exposed to a negative corona discharge in the dark and then was imagewise exposed through a positive original to form electrostatic latent images on the photosensitive paper. Then, after wetting the surface of the photosensitive paper with lsopar H containing no toner, the electro static latent images on the surface thereof were developed in the foregoing liquid developer [Time of Development: 20 seconds; a wire net was used as counter electrode], whereby sharp positive images having high image density were obtained. The maximum optical density of the images was 1.90.

Furthermore, when the same procedure as above was conducted after storing the liquid developer for 3 months at 35C, the maximum optical density of the images obtained was 1.78.

Gas-chromatography after the heat decomposition of toner, which had been washed repeatedly to remove carbon black, revealed the formation of decomposition products, which were identified as the components of compound (I) and (11).

EXAMPLE 2 The graft carbon copolymer prepared as in Example 1 was stored for 3 months at 35C and was dispersed in lsopar H in the same way as in Example 1 to provide a liquid developer. When a zinc oxide type photosensitive paper having electrostatic latent images was developed in the liquid developer, the maximum optical density of the images obtained was 1.86 and the images obtained were as sharp as those in Example 1.

COMPARISON EXAMPLE A graft carbon copolymer was produced as in Example 1 except that acrylamide was used in place of diacetone acrylamide. Then, a liquid developer was prepared using the graft copolymer in the same way as in Example 1 and further the same developing procedure as in Example 1 was conducted using the liquid developer. The maximum optical density of the images obtained was 1.85.

When the same developing procedure as above was conducted after storing the liquid developer for 3 months at 35C, the maximum optical density of the images was 1.69.

Also, the graft carbon copolymer obtained in the comparison example was stored for 3 months at 35C. It was the attempted to disperse the graft carbon copolymer in Isopar H by ultrasonic waves, but coagulation occurred and sufficient dispersion of the toner could not be obtained. Thus, 8 parts of the copolymer was kneaded together with 12 parts of a l 1 mixed solution of kerosene and toluene for 20 hours by means of ball mill and then the mixture was diluted with 1000 parts of Isopar to provide a liquid developer. When the developing procedure as in Example 1 was followed using the resulting liquid developer, the maximum optical density of the images obtained was 1.44.

EXAMPLES 3-7 Graft carbon copolymers were prepared using the components shown in Table 1 according to the manner of Example 1.

TABLE 1 Example Pigment Addition Polymerizable Compound (dispersing (Polarization monomer) control monomer) 3 carbon black lauryl methoxymethyl- (C-2, made by methacrylate acrylamide Asahi Carbon 60 parts 3.2 parts Co.) 36 parts 4 36 parts lauryl butoxymethyl- 40 parts methacrylate acrylamide 25 parts 4 parts Z-ethylhexyl methacrylate 25 parts 5 carbon black lauryl N-methylol (MA-8, made methacrylate acrylamide by Mitsubishi 19 parts 1 part Chemical Industry Co.) 18 parts Phthalocyanine Blue 2 parts 6 carbon black 19 parts morpholino- (C-2, made by 18.5 parts methylacrylamide Asahi Carbon 1.5 parts Co.) 20 parts 7 carbon black 18.5 pans acryloyl (MA-8, 36 parts morpholine Mitsubishi 3 parts Chemical Industry Co.) 20 parts When each of the graft carbon copolymers thus obtained was dispersed in Isopar G (the trade name of an isoparaffinic solvent made by Esso Standard Oil Co. having an aniline point of 80C, an initial boiling point of 158C, and a dry point of 177C), the toner was dispersed well in the solvent in each case. The toner was positively charged.

EXAMPLE 8 A liquid developer was prepared by diluting 4 parts of the graft carbon prepared in Example 4 with 1000 parts of Isopar G and thereafter 0.1 part of cobalt naphtenate was dissolved in the liquid developer. When the same developing procedure as in Example 1 was conducted using this liquid developer, good positive images of low streaking capability were obtained.

EXAMPLE 9 A liquid developer was prepared as in Example 1 except for using cyclohexane as the liquid carrier. When the same developing procedure as in Example 1 was conducted using this liquid developer, a rapid-drying developer was provided. The results were similar to those of Example 1.

EXAMPLE 10 A liquid developer was prepared as in Example 1 except for using kerosene as the carrier. When the same developing procedure as in Example 1 was conducted using this liquid developer, the developer was seen to show somewhat slower drying, but the cost thereof was extremely low, a significant commercial benefit. The results were otherwise similar to Example 1.

While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

What is claimed is:

1. A liquid developer for electrophotography comprising a carrier liquid having an electric resistance higher than about 10 0.0m. and a dielectric constant less than about 3, said carrier liquid having dispersed therein a toner prepared by graft polymerizing the addition polymerizable compound represented by formula (I) and the addition polymerizable compound represented by formula (11) onto pigment particles;

wherein R represents H or -Cl-l X represents COOC,.l-l +1 (6 s n s 20), R represents -H, and Y represents CONHCl-l Ol-I, CONl-lCl-l OCl-l CONl-lCl-1 OC H CONl-lCl-l OC l-l CONl-lC- H OC H the ratio of the addition polymerizable compound of formula (I) to the addition polymerizable compound of formula (II) being 5 45 parts by weight to 1 part by weight of the compound of the formula (ll); the size of the pigment particles being less than about l micron; and from about 0.1 to about 20 parts by weight of the toner being present per 1000 parts by weight of the carrier liquid.

2. The liquid developer for electrophotography as set forth in claim 1 in which the pigment is carbon black.

3. The liquid developer for electrophotography as set forth in claim 1 wherein the size of the pigment particles is less than 0.4 micron.

4. The liquid developer for electrophotography as set forth in claim 1 wherein from about 0.5 to about 10 parts by weight of the toner is present per 1000 parts by weight of the carrier liquid.

5. The liquid developer for electrophotography as set forth in claim 1 wherein the pigment particles are present in an amount less than about 6 parts by weight per 1 part by weight of the total amount of the compound of formula (I) and the compound of formula (11), but in an amount greater than about 0.2 parts by weight, same basis.

'CONH -C -CH -C -CH3, CONHCH N or CO N O tion 6. The liquid developer for electrophotography as set forth in claim 1 in which the formula (I) addition polymerizable compound is lauryl methacrylate and the formula (ll) addition polymerizable compound is diacetone acrylamide.

7. The liquid developer as set forth in claim 1 in which the formula (1) addition polymerizable compound is lauryl methacrylate and the formula (ll) addition polymerizable compound is methoxymethylacrylamide.

8. The liquid developer as set forth in claim 1 in which the formula (1) addition polymerizable compound is lauryl methacrylate and the formula (II) addipolymerizable compound is N- of said pigment is carbon black. 

1. A LIQUID DEVELOPER FOR ELECTROPHOTOGRAPHY COMPRISING A CARRIER LIQUID HAVING AN ELECTRIC RESISTANCE HIGHER THAN ABOUT 10**10 $.M. AND A DIELECTRIC CONSTANT LESS THAN ABOUT 3, SAID CARRIER LIQUID HAVING DISPERSED THEREIN A TONER PREPARED BY GRAFT POLYMERIZING THE ADDITION POLYMERIZABLE COMPOUND REPRESENTED BY FORMULA (I) AND THE ADDITION POLYMERIZABLE COMPOUND REPRESENTED BY FORMULA (II) ONTO PIGMENT PARTICLES;
 2. The liquid developer for electrophotography as set forth in claim 1 in which the pigment is carbon black.
 3. The liquid developer for electrophotography as set forth in claim 1 wherein the size of the pigment particles is less than 0.4 micron.
 4. The liquid developer for electrophotography as set forth in claim 1 wherein from about 0.5 to about 10 parts by weight of the toner is present per 1000 parts by weight of the carrier liquid.
 5. The liquid developer for electrophotography as set forth in claim 1 wherein the pigment particles are present in an amount less than about 6 parts by weight per 1 part by weight of the total amount of the compound of formula (I) and the compound of formula (II), but in an amount greater than about 0.2 parts by weight, same basis.
 6. The liquid developer for electrophotography as set forth in claim 1 in which the formula (I) addition polymerizable compound is lauryl methacrylate and the formula (II) addition polymerizable compound is diacetone acrylamide.
 7. The liquid developer as set forth in claim 1 in which the formula (I) addition polymerizable compound is lauryl methacrylate and the formula (II) addition polymerizable compound is methoxymethylacrylamide.
 8. The liquid developer as set forth in claim 1 in which the formula (I) addition polymerizable compound is lauryl methacrylate and the formula (II) addition polymerizable compound is N-methylolacrylamide.
 9. The liquid developer as set forth in claim 1 in which the formula (I) addition polymerizable compound is lauryl methacrylate and the formula (II) addition polymerizable compound is morpholinomethylacrylamide.
 10. The liquid developer as set forth in claim 1 in which the formula (I) addition polymerizable compound is lauryl methacrylate and the formula (II) addition polymerizable compound is acryloylmorpholine.
 11. The liquid developer for electrophotography as set forth in claim 1 where at least 90 percent by weight of said pigment is carbon black. 